Physics

• Types of light


  • Ultraviolet light
  • Infrared light
  • Visible light
• Ultraviolet light


  Used in sunlamps
• Infrared light


  Used in TV remotes to transfer signals to TV
• Visible light


  Light we can see with our eyes
• Sources of light


  • Luminous objects
  • Non-luminous objects
• Luminous objects


  Emit their own light
• Non-luminous objects


  Reflect light from another source
• Light travels faster than sound
• Light energy is transferred through space as electromagnetic waves in straight lines
• Light has wave-particle duality
• Rectilinear propagation of light


  • Light travels in straight lines
  • Rays of light form a beam of light
• Light reflects from an object


  The reflected light travels to our eyes
• Pinhole camera


  Image formed is upside down because of the way light propagates
• Shadows


  Absence of light due to a blockage in the path of light
• Light can bend around corners
• Shadows are formed due to rectilinear propagation of light and opaque objects
• Light on different surfaces


  Can be absorbed or reflected
• Characteristics of shadows: formed in the direction opposite to the light source, brighter light gives darker shadows, closer source of light gives bigger shadows, further away light is from object gives smaller shadows
• Absorption of light


  Light is absorbed by an object, only the colour of light that is not absorbed is seen
• White light is made up of seven colours
• Refraction


  Bending of light as it passes from one medium to another
• Primary colours of light


  Red, blue, green
• Secondary colours of light


  Cyan, magenta, yellow
• Black


  Unique, not a colour, all light is absorbed
• White


  All colours of light are reflected
• Reflection


  Bouncing of light off a surface
• Angle of incidence


  Angle between the incident ray and the normal to the surface
• Angle of reflection


  Angle between the reflected ray and the normal to the surface
• Real image vs Virtual image

  • Real image can be projected onto a screen, virtual image cannot
• Converging lens


  • Focuses light rays
  • Inverts the image
• Diverging lens


  • Spreads out light rays
  • Does not invert the image
• Clear image cannot be formed from light reflecting off a rough surface as light is scattered in many directions
• The SI unit of energy is the joule (J).